The present invention refers to centreless grinding machines of the type incorporating a frame, a regulating wheel carriage individually displaceably supported on guides in the frame and supporting a regulating wheel, a grinding wheel carriage individually displaceably supported on guides in the frame and supporting a grinding wheel, said regulating and grinding wheels between them defining a grinding gap of adjustable size, a work support provided in the grinding gap, and dressing means for the regulating and grinding wheels, said grinding and regulating carriages each being designed with at least two spaced apart supporting points relative to the guides.
The centreless grinding machine is traditionally used mainly for machining long series of workpieces. With today's demands for reduced stock-keeping there is a desire to be able to use the machine also for machining of shorter series.
When grinding a workpiece to desired measure between the grinding wheel and the regulating wheel under support from the work support provided in the grinding gap, heat is generated during the material removal, which heat primarily is transferred into the grinding wheel carriage and into the regulating wheel carriage. These carriages thereby are subjected to thermal expansion, whereby the size of the grinding gap between the grinding and regulating wheels is reduced. During continued grinding the heat will spread also to the machine frame, whereby the thermally conditioned, mutual movement of the grinding and regulating wheel carriages is compensated to a certain part. The thermal expansion of the grinding wheel carriage itself may amount to between 20 and 30 .mu.m, and as the demand for accuracy of the machined workpiece may amount to some few .mu.m, it is easy to understand that the conventional centreless grinding machine is not well suited for machining of short series of workpieces but needs a certain running-in time for reaching a steady state.
A purpose of the present invention is to provide a device at centreless grinding machines of the type described in the introduction, by means of which the above expressed problem with heat dependent alterations of the size of the grinding gap, is eliminated to a very high extent.
Another purpose of the invention is to render possible designing of shorter, and thereby less heavy and less space-requiring centreless grinding machines. These and other advantages, which will be apparent from the following description, have been achieved in that the said carriages are arranged in an overlap relation thus that one supporting point for one of the said carriages is situated between the two supporting points for the other carriage, for the purpose of compensating thermally dependent length variations at said carriages.
Hereinafter the invention will be further described with reference to embodiments shown in the accompanying drawings.